1. Field of the Invention
The present invention relates to a printed circuit board (PCB) including a predetermined circuit with a contact terminal electrically connected to the circuit, and the printed circuit board installed in an image forming apparatus. More particularly, the present invention relates to a printed circuit board having a contact terminal larger than a predetermined size comprising a group of small-area terminals, which conduct an electrical signal.
2. Description of the Related Art
Generally, electronic appliances comprise a printed circuit board (PCB) within the electrical appliance on which a circuit is mounted for controlling and processing operation of the electronic appliances. On the PCB are mounted circuit elements, and a contact terminal which is electrically connected to circuits external to the PCB.
For instance, image forming apparatuses such as printers, copiers, and multifunction office machines comprise a PCB as described above, and a consumables unit such as a developing unit and a photoconductive drum unit. The consumables units include a consumables unit terminal capable of allowing the exchange of signals with circuits within the consumables unit. When the consumables unit is mounted in the image forming apparatus, the consumables unit power terminal is supplied with power from a large-area contact terminal of the PCB. Power is supplied to the consumables by a moving pin contact in the main body of the image forming apparatus. In general, the moving pin contact is connected to the contact terminal of the PCB by a spring allowing for signal communications. By the elastic force of the spring, contact between the consumables unit power terminal and the moving pin allows the PCB to supply power to the consumables unit. Therefore, the contact terminal of the PCB has to have an enough surface area for the contact with the spring, and usually, a square terminal of about 7 mm to 12 mm in width is employed for this purpose. Hereinafter, the contact terminal of the above-described area of the PCB will be referred to as the large-area contact terminal for the convenience of explanation.
The large-area contact terminal provided on a conventional PCB can be fabricated by two methods. One is soldering a separate board-shaped metal terminal, and the other is using solder protrudingly applied on a board. When the board-shaped metal terminal is used for the large-area contact terminal, contact efficiency is superior, however, manufacturing cost increases. On the other hand, when using solder for the contact terminal, the manufacturing cost is relatively low.
FIGS. 1A and 1B illustrate the PCB 20 having the large-area contact terminal 21 formed by the solder, and a contact point of the PCB 20. As shown in FIGS. 1A and 1B, the large-area contact terminal 21 is formed by applying the solder to a predetermined area terminal on a rear surface of the printed circuit board 20 corresponding to a circuit element 27 mounted on the printed circuit board 20.
However, it is difficult using solder to form the large-area contact terminal 21 as above with a uniform thickness because the large-area contact terminal 21 is too wide, and the solder is input as a liquid. Therefore, the surface of the large-area contact terminal 21 becomes uneven. As a reference, a general soldering process creating a solder pattern width of approximately 2 mm typically guarantees a uniform thickness of solder. Accordingly, poor contact occurs between the large-area contact terminal 21 and an external terminal 30 due to the area of the large-area contact 21 being greater than 2 mm and the subsequent unevenness of the solder.
Other conventional solutions to the solder unevenness include forming a pattern on the PCB 20 without soldering, or soldering the pattern with a tape masking. However, in case of the former, the pattern is easily eroded. In case of the latter, when the tape is removed, solder remnants can be formed. This causes unstable contact between the large-area contact terminal 21 and the external terminal 30. Additionally, the manufacturing process is complicated and is costly.